1428438 - Cannot use WebGLBuffer as key to WeakMap

Status: RESOLVED DUPLICATE of bug 1351501

(Core :: DOM: Bindings (WebIDL), defect)

Description

[Josh Mize [:jgmize]]

I first came across this in https://github.com/oussama/webgl-rs/issues/1 with steps to replicate copied from my commment there:


var canvas = document.createElement('canvas')
var ctx = canvas.getContext('webgl')
var buffer = ctx.createBuffer()
var weakMap = new WeakMap()
weakMap.set(buffer, 'some value')


Results in the following error on Firefox Nightly:
TypeError: cannot use the given object as a weak map key

The same code works in current chrom{e,ium} for me.

Comment 1

[jice.nospam]

Issue still present in firefox 58.0.2 : http://og.tn/webgl-rs/example/bin/simple/

Yet, buffer is an object, so it should be valid as a weakmap key : 

    >> var canvas = document.createElement('canvas')
       var ctx = canvas.getContext('webgl')
       var buffer = ctx.createBuffer()
    undefined
    >> buffer
    WebGLBuffer {  }
    >> typeof buffer
    "object"

Comment 2

[Andrew Osmond [:aosmond] (he/him)]

WebGLBuffer is a normal WebIDL object, implements nsWrapperCache, so I would have expected the JS engine to accept it.

Comment 3

[André Bargull [:anba]]

The error mentioned in comment #0 is thrown from here [1], so it indicates that the "Preserve Wrapper Callback" cannot handle WebGLBuffer objects. The relevant "Preserve Wrapper Callback" is defined here [2], so it actually looks like a DOM issue?

[1] https://searchfox.org/mozilla-central/rev/55da592d85c2baf8d8818010c41d9738c97013d2/js/src/builtin/WeakMapObject-inl.h#27-30
[2] https://searchfox.org/mozilla-central/rev/55da592d85c2baf8d8818010c41d9738c97013d2/dom/bindings/BindingUtils.cpp#1149-1168

Comment 4

[André Bargull [:anba]]

Jon, do you think it makes sense to move this bug (and other similar bugs like bug 1489145, bug 1449485, and bug 1351501) to the DOM component, because it seems this is something which needs to be handled in DOM code?

Comment 5

[Jon Coppeard (:jonco)]

Yes, I think that makes sense.  Passing on the NI to Andrew who wrote TryPreserveWrapper().

Comment 7

[Andrew McCreight [:mccr8]]

Thanks for finding all of these dupes, anba.